Figure 4. Modulation of NHE activity by a PKA agonist/antagonist.

Na⁺-H⁺ exchange activity was assessed as initial rates of HOE694 inhibitable pH_i recovery of A6 cell cultures from an acid load as described in Fig. 3. To test the effect of 8-bromo-cAMP (PKA agonist) and/or H89 (PKA antagonist), cell cultures were repetitively acidified to the same starting acid pH_i value, and pH_i recovery rates were observed either in the absence or presence of pharmacological agents added to the apical and basolateral cell surface. In all experiments, cells were exposed to different agents for 15 min prior to evaluating their effect on Na⁺-H⁺ exchange activity in the absence or presence of HOE694 that was included for a 2 min period in the apical perfusate. The number of experiments performed under identical experimental conditions is given in parentheses. ap, the change (expressed in %) of the activity of apical Na⁺-H⁺ exchanger in response to pharmacological agents; bl, the corresponding change (expressed in %) of basolateral Na⁺-H⁺ exchanger; HOE694 ‘resistant’, agonist-induced net change (expressed in %) of apical transport activity which was calculated as difference between the sum of Na⁺-dependent rate of pH_i recovery measured in the presence of agonists and 10⁻⁴ M apical HOE694 and 10⁻⁴ M apical HOE694 alone. * Significant vs. control;⁺ significant vs. HOE694;. significant vs. 8-bromo-cAMP; ▴ significant vs. 8-bromo-cAMP plus HOE694.